Carrier 69NT40-541-300, Операция и обслуживание, Страница: 106 / 152

6 − 18 T − 318
j. Frozen operation: In frozen mode the valve tends to
stay open as much as possible. Again, this is depen-
dent upon current limit setting and control logic. Turn
the unit OFF and ON, as in the perishable mode, and
watch the gauges. The valve will run at 21% open if
CREL logic is active, and will open to maximum allow-
able after this. Depending on ambient conditions,
there should be an increase in suction pressure and
current draw as the valve opens. However, at times,
this may be difficult to fully determine.
k. If the unit still does not operate properly, stop unit and
proceed to the following step to check out the SMV
system.
6.20 VALVE OVERRIDE CONTROLS
Cd41 is a configurable function code that allows manual
operation of the SMV valve for troubleshooting. Test se-
quences are provided in Table 6-1.
PCnt (% Setting
− SMV Capacity Modulation) allows
opening of the SMV to various percentages.
The Override Timer (tIM) selection is provided to enter a
time period of up to five minutes, during which the over-
ride is active. If the timer is active, the valve override se-
lection will take place immediately. If the timer is not ac-
tive, changes will not take place for a few seconds after
the timer is started. When the timer times out, override
function is automatically terminated and the valve re-
turns to normal machinery control. To operate the over-
ride, do the following:
a. Press the CODE SELECT key then press an AR-
ROW key until Cd41 is displayed in the left window.
The right window will display a controller communica-
tions code.
b. Press the ENTER key. The left display will show a test
name alternating with the test setting or time remain-
ing. Use an ARROW key to scroll to the desired test.
Press the ENTER key and SELCt will appear in the
left display.
c. Use an ARROW key to scroll to the desired setting,
and then press the ENTER key. Selections are pro-
vided in the following table.
d. If the timer is not operating, follow the above proce-
dure to display the timer. Use an ARROW key to scroll
to the desired time interval and press ENTER to start
the timer.
e. The above described sequence may be repeated
during the timer cycle to change to another override.
Table 6-1 Valve Override Control Displays
Left Display Controller Communications Codes
(Right Display)
Setting Codes (Right Display)
Cd 41/SELCt tIM
(Override Timer)
0 00 (0 minutes/0 Seconds)
In 30 second increments to
5 00 (5 minutes/ 0 seconds)
PCnt
(% Setting − SMV Capacity Modulation)
AUtO
(Normal Machinery Control)
0
3
6
10
25
50
100
6.20.1 Checking the Stepper Valve
a. Checking with ohmmeter
Stop the unit, disconnect the 4-pin connector to the
stepper SMV. With a reliable digital ohmmeter, check
the winding resistance. In normal ambient, the valve
should have 72 to 84 ohms measured on the red/green
(a-b terminals) and on the white/black (c-d terminals)
leads. If an infinite or zero reading occurs, check
connections and replace the motor. If near normal or
normal reading occurs, proceed to step 6.20.2 to check
out the controller.
b. Checking with SMA-12 portable stepper drive tester
The SMA-12 portable stepper drive tester (Carrier
Transicold P/N 07-00375-00) is a battery − operated
stepper drive that will open and close the SMV, allowing
a more thorough check of the motor.
1. Stop the unit, disconnect the 4-pin connector from
the stepper module to the valve (see Figure 6-23)
and attach the SMA-12 stepper drive to the connec-
tor going to the valve.
2. Set the SMA-12 pulse per second (PPS) to one PPS
and either open or close valve. Each LED should
light sequentially until all four are lit. Any LED failing
to light indicates an open on that leg, which indicates
a poor connection or an open coil. Repair or replace
as required to achieve proper operation.
3. Restart unit, set the step rate to 200PPS on SMA-12
for the valve, and close stepper valve while watching
the suction gauge. Within one minute the suction
pressure will go into a vacuum. This is an indication
that the valve is moving.